Stock 930 engines are cammed to achieve best torque trough middle range. Turbocharger is somewhat big as well and goes "online" after 3000 RPM. As such, torque will raise just north of 3000 RPM and then start falling further up the revs.

At 5500 RPM, torque will fall quicker than revs rize as cams run out of breath, and power curve will start going down again.
With other words, engine isn't "dead" after 5500 RPM but it's often not worth it revving much past that.

As optimal accelleration is achieved by highest sum of areas under power curve and 930 box is somewhat long-legged, one needs to slightly oveshoot 5500 RPM's when shifting. This in order to hit the "sweetspot" on next gear.

To truly enhance the 930 engine's ability to rev, one would need to swap the turbocharger to better/bigger one, change the cams to more radical profile and get rid of CIS.